Shield pole perpendicular magnetic recording (PMR) writers are commonly used in current PMR (hard disk drive) HDD products. PMR writers have become the mainstream technology for disk drive applications beyond 200 Gbit/in2, replacing longitudinal magnetic recording (LMR) devices. Due to the continuing reduction of transducer size, high moment soft magnetic thin films with a Bs above 22 kG are required for write head applications. A PMR head combines the features of a single pole writer and a soft magnetic underlayer to offer a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density. In particular, a shielded pole head can provide a large head field gradient at the trailing side due to the presence of a trailing shield and substantially improve the write performance.
Referring to FIG. 1, a conventional PMR main pole layer is depicted from a top view or down-track perspective. One end of the main pole layer is formed along an air bearing surface (ABS) plane 6-6 that is positioned above a magnetic recording medium (not shown). The PMR writer moves along the ABS during a write operation. The main pole layer 3 is comprised of a write pole 3a that terminates in a pole tip 3t at the ABS 6-6, and a yoke 3b that flares outward at an angle θ from the end of the write pole opposite the ABS. The end of the write pole 3a lies along the plane 7-7 that is a neck height (NH) distance from the ABS. The intersection of the yoke 3b and write pole 3a is at the neck 8. Trailing and side shields are not shown in order to simplify the drawing.
In perpendicular recording, the main write pole footprint typically has a trapezoidal shape where the write pole width is greater at the trailing edge than at the leading edge to compensate for the skew effect as depicted in FIG. 2b. For example, write pole WP1 shown in FIG. 2a has a leading edge LE with width e equal to that of a trailing edge TE. As the write pole WP1 moves in a z-direction or down-track, the erase band EB1 has a substantial width in the cross-track direction. On the other hand, write pole WP2 in FIG. 2b has an LE with a smaller width e1 that width e2 for the TE. As a result, the erase band EB2 is significantly smaller in the cross-track direction than EB1 which leads to fewer unintended side track erasures and improved performance.
Referring to FIG. 3, another concern in PMR writing is that when a main pole layer is plated to fill an opening and form a write pole 10 with a trapezoidal shape, subsequent processing such as a chemical mechanical polish (CMP) method is used to planarize the top surface which reduces the thickness of write pole and main pole layer 11 from t1 to t2. However, this process introduces a write pole width variation since the top surface 10a after CMP has a smaller width than that of top surface 10b before CMP due to the sloped sidewalls 10s. This source of variation has been overcome in a dry-film based process where the main pole layer is formed by first sputtering a full film followed by an ion-milling process to define the pole shape. Since the top of the write pole and main pole layer is protected during the milling process, the write pole thickness is determined by the initial sputtered film thickness and can be controlled very well.
Referring to FIG. 4, in order to meet the high demand of writability at very narrow track widths, write poles with a trailing edge taper (tWG) have been implemented. A tapered write pole is typically formed by first fabricating a thicker pole (FIG. 4 top) with a trapezoidal bevel angle already defined such that sloped sidewalls 20s are aligned at a bevel angle (BA) α in FIG. 5 with respect to a plane that is perpendicular to the bottom surface of the write pole. Then a tWG ion milling process is applied to create a trailing edge taper as in FIG. 4 bottom. Note that the top surface 20t of the main pole layer is sloped such that the end of the write pole at the ABS has a smaller thickness than at the back end 20n of the write pole where it adjoins the yoke 20y. The taper generally extends beyond the back end 20n and into the portion of the yoke 20y by a distance f. Unfortunately, since the write pole along the ABS retains a trapezoidal shape, there is still substantial write pole width variation as a function of variations in write pole thickness at the ABS. In addition, the ion milling process introduces another variable that affects pole width. For example, write pole width w1 along top edge 20b at the ABS before tapering shrinks to w2 along top edge 20a at the ABS in the tapered structure where w2−w1 may vary greatly depending on the taper angle δ in FIG. 5. Therefore, even a dry film process is no longer immune to pole width variations because the final ABS pole width is defined by the tWG ion milling and not by the initial write pole thickness in FIG. 4 (top).
The ABS pole width is also subject to a lapping variation during the slider fabrication process. As shown in FIG. 5, pole width variation may be represented as ΔPWA where ΔPWA=PWA′−PWA=2×Δh×tan(BA) where BA is also depicted as angle α and Δh is the pole height variation. For a lapping induced neck height change (ΔNH), the equation above may be further represented as ΔPWA=PWA′−PWA=2×Δh×tan(BA)=2×(ΔNH)×tan(tWGa)×tan(BA) where tWGa is the trailing edge taper angle δ. For a nominal trailing edge taper angle δ=30 degrees and a trapezoidal bevel angle α=15 degrees, a 40 nm range (±20 nm) of lapping variation will result in a 12 nm variation (ΔPWA) for ABS pole width which is significant amount when considering pole width is typically about 100 nm for advanced PMR writers. In the ABS view, 20t is the top slope of the tapered portion between the top edge 20h and the edge 20a or 20a′ corresponding to PWA or PWA′, respectively, where the tapered top surface adjoins the ABS. Note in the cross-section view that when the lapping stops along sidewall 20s, the top edge 20a of the write pole along the ABS will have a width PWA. If the lapping proceeds further and removes a portion of write pole 20p between sidewall 20s at the initial ABS and sidewall 20s′ along the new ABS (not shown), then the top edge 20a′ will have a width PWA′ greater than PWA.
In U.S. Pat. No. 7,313,863, Headway disclosed a so called “pencil” writer with no tapered edge such that the main pole layer thickness c is constant from the pole tip 30p at the ABS to the back end of the main pole layer including yoke 30y. A key feature is a zero bevel angle at a trailing portion 30e including trailing side 30b while the leading portion 30d including leading side 30f retains a trapezoidal shape as shown from an oblique view (FIG. 6a) and ABS view (FIG. 6b). Thus, the ABS pole width of this head is less sensitive to CMP variations illustrated in FIG. 3.
In addition, U.S. Patent Application No. 2006/0044677 from Headway describes a similar write pole structure having a rectangular shape with straight side walls at the trailing edge and a trapezoidal shape near the leading edge. However, an improved design is still needed that reduces sensitivity of ABS pole width to a trailing edge taper milling process and to back end lapping processes while maintaining the advantage of enhanced writability provided by a trailing edge tapered main pole.
U.S. Pat. No. 7,430,095 describes a trapezoidal shaped write pole with a tapered leading edge to reduce skew effects.
U.S. Pat. No. 7,253,992 discloses an ion milling method to form a main pole having a leading edge taper.
In U.S. Pat. No. 7,296,338, a trapezoidal write pole having a trailing edge taper is formed by an ion milling process.